BAGHDAD - Iraqi troops battled to dislodge an al-Qaida splinter group from the city of Tikrit on Monday after its leader was declared caliph of a new Islamic state in lands seized this month across a swathe of Iraq and Syria.

Alarming regional and world powers, the Islamic State in Iraq and Syria (ISIS) claimed universal authority, declaring its leader Abu Bakr al-Baghdadi was now caliph of the Muslim world - a medieval title last widely recognized in the Ottoman sultan deposed 90 years ago after World War One.

"He is the imam and caliph for Muslims everywhere," group spokesman Abu Muhammad al-Adnani said in an online statement on Sunday, using titles that carry religious and civil power.